Aeroplane-propeller blade



W. A. LORENZ.

Patented Dec. 7, 1920.

chum we B5 2 EV L u J DID 0E RI- DIF. EN No u PC H P. AA

be destructive.

UNITED STATES WILLIAM A. LORENZ, OF HARTFORD, CONNECTICUT.

AEROPLANE-PROPELLER BLADE.

Specification of Letters Patent.

Patented Dec. 7, 1920.

Application filed July 25, 1918. Serial No. 246,627.

To all whom it may concern:

Be it known that I, WILLIAM A. LORENZ, a citizen of United States, residing at Hartford, in the county of Hartfordand State of' Connecticut, have invented new and useful Improvements in Aeroplane-Propeller Blades, of which the following is a specification.

Aeroplane propellers have been made of Wood and of metal.\ The wooden propeller blades at the present time seem to bepreferable because of their flexibility and their lightness. These blades are preferably made of black walnut or of mahogany. They are properly shaped, carefully balanced and varnished.

It is found that by building up a wooden propeller of numerous slabs, there is not apt to be great concentration of weight or density in any one spot or region; or, in other words, the irregularities of weight are more distributed or scattered. If it were all a single piece of wood, the excess of weight might be all at one portion of the propeller, and'this would of course prove fatal to the use of the propeller at the high speeds demanded, since an imperfectly balancedweight revolving at such high speed would This fault, although partially overcome by building in layers, is still so serious that an enormously large percentage of wooden propellers is discarded or wasted at the outset, because of the failure of skilled artisansto overcome their inherently unbalanced condition:

Besides the difficulty with the balancing, there is a further difliculty with wooden'propellers due tothe weakness at the hub thereof, arising from the existence of the grain in the Wood, which is necessarily fragile at the sides of the hub where the grain is in tangential direction, so that the wood is liable to split. Even though by building the propeller up of layers there may be arranged some crossing of the grain in the different layers, still this does not overcome'the weak-' ness of the hub; and it has been found necessary, therefore, to make the hub unduly large in endeavoring to overcome this weakness. The entire wooden propeller has to be made unduly thick to reduce liability of splitting. This thickness of the hub and blades conducesto inefficiency, and it becomes necessary to revolve the propeller at such high speed as to be dangerous.

duce a propeller which Another difiiculty arises from the inherent grain of the Wood, which is easily split. Hence, a sudden increase of air resistance at a certaln part of the blade'may overcome the resistance of the wood, and split it from end to end.

The Wooden propeller blades are particularly liable to damage from accidents, or durlng an attackby rifle bullets; the striking of a propeller blade in a tree, or the striking of a propeller blade against any obstruction, will damage that blade, and in many cases render it entirely useless. If a bullet is fired at a wooden propeller and strikes a blade, the result is that the blade splits from end to end, and, of course, owing to air resistance the blade breaks off, and the remaining blade is of course rendered useless, and in fact becomes a source of dan er because of its unbalanced condition. nother objection to the -wooden propeller blade consists of the fact that it is quite flexible and it bends out of alinement. This bending may be unequal on the blades, if the wood is of unequal density.

Owing to their variation in density in different regions, the wooden blades are apt to bend differently when revolving at high speeds and hence subject to great air pressure, so that the blades will revolve in different planes, thus developing irregularity in striking the air, reducing'their efficiency, making it necessary to drive them dangerously fast, and roducing highly objectionable noise. oreover, the aeroplane is largely used for photography, in which much depends upon the steadiness ,of'the machine, so that the practically unavoidable slightly unbalanced condition of the wooden propeller produces at high speed a sharp vibration, which proves an impediment in securing proper photographs. The making of propeller blades in laminations requires very careful gluing and very careful workmanship, and the expense of shaping theblades and balancing them is large; v

The whirring noise of wooden propeller blades is very considerable, and any improvement that will reduce this noise is desirable. The objects of the invention are, to overcome these objections and avoid the enormous condemnation and waste of product in manufacturing aeroplane propellers, to prois practically selfbalancing, to reduce or avoid the danger involved in driving the propellers at the terrific speed heretofore necessary, to instruck by a bullet, to increase the photographing efliciency, and substantially to reduce the noise of operation.

I produce a propeller which may be all in a single piece of homogeneous material of uniform density throughout, is inherently free of unbalanced portions, and does not possess the fatal drawback of wooden propellers, which is only partly overcome by building them up in layers. However, these blades may be made separately, all alike and joined to a metal hub.

This propeller may be made with thin air-cutting blades, which may be compared to knife blades, and since the hub is not subject to difficulties from the use of material having a splitting grain, such as wood, it may be made. of normal size,'that is, relatively small as compared with a wooden hub. Efiiciency of the propeller is thus so far increased that it may be run at much slower speed than a wooden propeller of the same length. Or the novel propeller may be made with shorter blades. In either case a great gain is made in the matter of safety; and lower speed also conduces to reduction or avoidance of trouble from slightly unbalanced conditions, the trouble from which increases as the square of the speed. If enough sudden resistance is encountered to start a break in the novel propeller, it will not act like wood and split apart the moment that its initial resistance is overcome, but it will continue all the way to the end in resisting the effort of the air to increase the length of the break. In other words, the wood splits all at once, only necessary to overcome the initial re sistance; whereas my novel device constantly resists at every step of the break. Hence the wooden propeller will suddenly collapse, whereas the novel propeller would not collapse, but would continue to resist the disrupting force, and even at the worst would only be slowly suffer a gradual reduction of efficiency.

A bullet striking the blade of the novel propeller in the same place as in the old wooden propeller, will not split the blade from end to end, but owing to the consistency of the vulcanized fiber the bullet will only be apt to punch a hole through the blade Without splitting it; or if the bullet strikes near the edge, it will simply chip off a small portion of that edge, without severing or splitting the blade. The propeller wil therefore continue usable and quite eflicient.

it being overcome thereby and only I construct a propeller by making a metallic hub, and attaching thereto, propeller blades made of vulcanized fiber or similar material. Instead of using metallic hubs I may also make the hub and the blades in one piece. propeller blade may be attached to the propeller shaft by keys or in any other suitable manner.

Vulcanized fiber weighs somewhat more than heaviest mahogany, and because vulcanized fiber is extremely tough it can be made smaller in cross section than when made of wood. Vulcanized fiber is stiff; is very tough, and will withstand considerable shock before it gives way.

Comparing the action of a model propeller blade of black walnut with a similar one made of vulcanized fiber,"I find the following advantages, which attach to the use of vulcanized fiber. 1 I

The wooden blades are deflected to a considerable extent, when running at speed. In

a vulcanized fiber propeller made in the same section as a wooden propeller, the fiber blades did not show any perceptible deflection. Consequently the blades retain their shape at high speed much more readily than does wood. As vulcanized fiber is uniform in texture, the blades may be balanced more readily than if made of wood, which may be-more or less dense in one blade than in the opposite blade.

In my tests, it is also found that the efiiciency of the vulcanized fiber blade in producing a current of air through a test gate is greater than that of wood; that the vulcanized fiber blade blows the gate open to a greater extent than does the wooden blade.

Vulcanized fiber being tougher than wood, the edges of the blades may be made considerably sharper, and the body of the blades thinner than if made of wood, and will cut the air more easily than a blunter shaped wooden blade, which adds to the efliciency of such a propeller.

Any one of'these advantages would in practice he a great gain in a propeller made of fiber as indicated.

A propeller of vulcanized fiber can be made to the proper contour under a very powerful hydraulic press. The central hole, and the keyways, and the hub, and the blades, could all be pressed in the mold, leaving but a little flash on the edges of the propeller, to be trimmed off.

In the drawings Figure 1 represents a central sectional side view through the hub and the blades of the propeller. Fig. 2 represents a rear'view of Fig. 1 showing only the propeller. Fig. 3 represents a'sectional view of a propeller in which the wings and the hub are made in one piece.

In the drawings,5 shows a portion of an aeroplane, and 6, the propeller shaft. 7 is geneous the metallic hub keyed to the shaft; 8 represents a Washer, and 9, bolts or rivets, While 10 represents the propeller itself. This propeller is secured to the hub by means of bolts, Washer and a nut.

Fig. 3 shows a propeller shaft 12, and the propeller blades 13l3, and hub 14, made in one piece. This hub l l'is grooved and keyed to the shaft, or may be attached in any other way. A Washer and nut 15 may be used to hold the propeller blade on the shaft. This molded propeller can be readily trimmed to gage at the edges. It can be varnished and polished, so as to present a comparatively frictionless surface to the air.

I claim the followin 1. A shock-resisting propeller for aeroplanes, comprising a set of integral opposing blades made in one piece and composed of tough rigid vulcanized fiber of homotexture and uniform density throughout.

2. A shock-resisting propeller for aeroplanes. comprising a set of integral opposing thinned blades made in one piece and having keen air-cutting portions and composed of tough rigid vulcanized fiber of homogeneous texture and uniform density throughout.

A shock-resisting propeller for aeroplanes. comprising a set of integral opposing thinned blades made in one piece and having keen air-cutting portions and composed of tough rigid vulcanized fiber of homogeneous texture and uniform density throughout, andvarnished to prevent deterioration of its substance from moisture.

4. A shock-resisting propeller for aeroplanes. comprising a set of integral opposing blades made in one piece and having keen air-cutting portions and composed of tough rigid vulcanized fiber of homogeneous texture and uniform density throughout, said propeller comprising hub and shank portions integral with said blades.

5. A shock-resistin propeller for aeroplanes, comprising a set of integral opposing blades molded under pressure in one.

piece and composed of tough rigid vulcanized fiber of homogeneous texture and uniform density throughout.

(3. A set of opposing thinned blades, each made in one piece and having keen air-cutting portions, and a metal hub joining said blades into a shock-resisting propeller for aeroplanes, said blades composed of tough rigid vulcanized fiber which is of homogeneous texture and uniform density throughout all the blades.

7. A shock-resisting propeller for aeroplanes, comprising a setof connected opposing thinned blades each made in one piece and having keen air-cutting portions and composed of tough rigid vulcanized fiber which is of homogeneous texture and uniform density throughout all of said blades.

8. A shock-resisting thinned blade for an aeroplane propeller. having keen air-cutting portions and composed ofa single piece of WILLIAM A. LORENZ. 

